26 Algorithms library [algorithms]

26.8 Sorting and related operations [alg.sorting]

26.8.5 Partitions [alg.partitions]

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template<class InputIterator, class Predicate> constexpr bool is_partitioned(InputIterator first, InputIterator last, Predicate pred); template<class ExecutionPolicy, class ForwardIterator, class Predicate> bool is_partitioned(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Predicate pred); template<input_iterator I, sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> constexpr bool ranges::is_partitioned(I first, S last, Pred pred, Proj proj = {}); template<input_range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> constexpr bool ranges::is_partitioned(R&& r, Pred pred, Proj proj = {}); template<execution-policy Ep, random_access_iterator I, sized_sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> bool ranges::is_partitioned(Ep&& exec, I first, S last, Pred pred, Proj proj = {}); template<execution-policy Ep, sized-random-access-range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> bool ranges::is_partitioned(Ep&& exec, R&& r, Pred pred, Proj proj = {});
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Let proj be identity{} for the overloads with no parameter named proj.
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Returns: true if and only if the elements e of [first, last) are partitioned with respect to the expression bool(invoke(pred, invoke(proj, e))).
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Complexity: Linear.
At most last - first applications of pred and proj.
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template<class ForwardIterator, class Predicate> constexpr ForwardIterator partition(ForwardIterator first, ForwardIterator last, Predicate pred); template<class ExecutionPolicy, class ForwardIterator, class Predicate> ForwardIterator partition(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Predicate pred); template<permutable I, sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> constexpr subrange<I> ranges::partition(I first, S last, Pred pred, Proj proj = {}); template<forward_range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires permutable<iterator_t<R>> constexpr borrowed_subrange_t<R> ranges::partition(R&& r, Pred pred, Proj proj = {}); template<execution-policy Ep, random_access_iterator I, sized_sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> subrange<I> ranges::partition(Ep&& exec, I first, S last, Pred pred, Proj proj = {}); template<execution-policy Ep, sized-random-access-range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires permutable<iterator_t<R>> borrowed_subrange_t<R> ranges::partition(Ep&& exec, R&& r, Pred pred, Proj proj = {});
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Let proj be identity{} for the overloads with no parameter named proj and let E(x) be bool(invoke(​pred, invoke(proj, x))).
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Preconditions: For the overloads in namespace std, ForwardIterator meets the Cpp17ValueSwappable requirements ([swappable.requirements]).
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Effects: Places all the elements e in [first, last) that satisfy E(e) before all the elements that do not.
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Returns: Let i be an iterator such that E(*j) is true for every iterator j in [first, i) and false for every iterator j in [i, last).
Returns:
  • (7.1)
    i for the overloads in namespace std.
  • (7.2)
    {i, last} for the overloads in namespace ranges.
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Complexity: Let :
  • (8.1)
    For the non-parallel algorithm overloads, exactly N applications of the predicate and projection.
    At most swaps if the type of first meets the Cpp17BidirectionalIterator requirements for the overloads in namespace std or models bidirectional_iterator for the overloads in namespace ranges, and at most N swaps otherwise.
  • (8.2)
    For the parallel algorithm overloads, swaps and applications of the predicate.
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template<class BidirectionalIterator, class Predicate> BidirectionalIterator constexpr stable_partition(BidirectionalIterator first, BidirectionalIterator last, Predicate pred); template<class ExecutionPolicy, class BidirectionalIterator, class Predicate> BidirectionalIterator stable_partition(ExecutionPolicy&& exec, BidirectionalIterator first, BidirectionalIterator last, Predicate pred); template<bidirectional_iterator I, sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> requires permutable<I> constexpr subrange<I> ranges::stable_partition(I first, S last, Pred pred, Proj proj = {}); template<bidirectional_range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires permutable<iterator_t<R>> constexpr borrowed_subrange_t<R> ranges::stable_partition(R&& r, Pred pred, Proj proj = {}); template<execution-policy Ep, random_access_iterator I, sized_sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> requires permutable<I> subrange<I> ranges::stable_partition(Ep&& exec, I first, S last, Pred pred, Proj proj = {}); template<execution-policy Ep, sized-random-access-range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires permutable<iterator_t<R>> borrowed_subrange_t<R> ranges::stable_partition(Ep&& exec, R&& r, Pred pred, Proj proj = {});
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Let proj be identity{} for the overloads with no parameter named proj and let E(x) be bool(invoke(​pred, invoke(proj, x))).
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Preconditions: For the overloads in namespace std, BidirectionalIterator meets the Cpp17ValueSwappable requirements ([swappable.requirements]) and the type of *first meets the Cpp17MoveConstructible (Table 31) and Cpp17MoveAssignable (Table 33) requirements.
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Effects: Places all the elements e in [first, last) that satisfy E(e) before all the elements that do not.
The relative order of the elements in both groups is preserved.
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Returns: Let i be an iterator such that for every iterator j in [first, i), E(*j) is true, and for every iterator j in the range [i, last), E(*j) is false.
Returns:
  • (12.1)
    i for the overloads in namespace std.
  • (12.2)
    {i, last} for the overloads in namespace ranges.
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Complexity: Let N = last - first:
  • (13.1)
    For the non-parallel algorithm overloads, at most swaps, but only swaps if there is enough extra memory.
    Exactly N applications of the predicate and projection.
  • (13.2)
    For the parallel algorithm overloads, swaps and applications of the predicate.
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template<class InputIterator, class OutputIterator1, class OutputIterator2, class Predicate> constexpr pair<OutputIterator1, OutputIterator2> partition_copy(InputIterator first, InputIterator last, OutputIterator1 out_true, OutputIterator2 out_false, Predicate pred); template<class ExecutionPolicy, class ForwardIterator, class ForwardIterator1, class ForwardIterator2, class Predicate> pair<ForwardIterator1, ForwardIterator2> partition_copy(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, ForwardIterator1 out_true, ForwardIterator2 out_false, Predicate pred); template<input_iterator I, sentinel_for<I> S, weakly_incrementable O1, weakly_incrementable O2, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> requires indirectly_copyable<I, O1> && indirectly_copyable<I, O2> constexpr ranges::partition_copy_result<I, O1, O2> ranges::partition_copy(I first, S last, O1 out_true, O2 out_false, Pred pred, Proj proj = {}); template<input_range R, weakly_incrementable O1, weakly_incrementable O2, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires indirectly_copyable<iterator_t<R>, O1> && indirectly_copyable<iterator_t<R>, O2> constexpr ranges::partition_copy_result<borrowed_iterator_t<R>, O1, O2> ranges::partition_copy(R&& r, O1 out_true, O2 out_false, Pred pred, Proj proj = {}); template<execution-policy Ep, random_access_iterator I, sized_sentinel_for<I> S, random_access_iterator O1, sized_sentinel_for<O1> OutS1, random_access_iterator O2, sized_sentinel_for<O2> OutS2, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> requires indirectly_copyable<I, O1> && indirectly_copyable<I, O2> ranges::partition_copy_result<I, O1, O2> ranges::partition_copy(Ep&& exec, I first, S last, O1 out_true, OutS1 last_true, O2 out_false, OutS2 last_false, Pred pred, Proj proj = {}); template<execution-policy Ep, sized-random-access-range R, sized-random-access-range OutR1, sized-random-access-range OutR2, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires indirectly_copyable<iterator_t<R>, iterator_t<OutR1>> && indirectly_copyable<iterator_t<R>, iterator_t<OutR2>> ranges::partition_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR1>, borrowed_iterator_t<OutR2>> ranges::partition_copy(Ep&& exec, R&& r, OutR1&& out_true_r, OutR2&& out_false_r, Pred pred, Proj proj = {});
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Let proj be identity{} for the overloads with no parameter named proj and let E(x) be bool(invoke(​pred, invoke(proj, x))).
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For the overloads with no parameters last_true, last_false, out_true_r, or out_false_r, let
  • (15.1)
    M be the number of iterators in [first, last) for which E(i) is true, and K be last - first;
  • (15.2)
    last_true be out_true + M, and last_false be out_false + K.
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For the overloads with parameters last_true, last_false, out_true_r, or out_false_r, let M be last_true last_true - out_true and K be last_false - out_false.
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Let:
  • (17.1)
    i1 be the iterator in [first, last) for which E(*i1) is true and there are exactly M iterators j in [first, i1) for which E(*j) is true, or last if no such iterator exists;
  • (17.2)
    i2 be the iterator in [first, last) for which E(*i2) is false and there are exactly K iterators j in [first, i2) for which E(*j) is true, or last if no such iterator exists;
  • (17.3)
    N be min(i1 - first,  i2 - first).
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Mandates: For the overloads in namespace std, the expression *first is writable ([iterator.requirements.general]) to out_true and out_false.
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Preconditions: The input range and output ranges do not overlap.
[Note 1: 
For the parallel algorithm overload in namespace std, there can be a performance cost if first's value type does not meet the Cpp17CopyConstructible requirements.
For the parallel algorithm overloads in namespace ranges, there can be a performance cost if first's value type does not model copy_constructible.
— end note]
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Effects: For each iterator i in [first, first + N), copies *i to the output range [out_true, last_true) if E(*i) is true, or to the output range [out_false, last_false) otherwise.
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Returns: Let o1 be the iterator past the last copied element in the output range [out_true, last_true), and o2 be the iterator past the last copied element in the output range [out_false, last_false).
Returns:
  • (21.1)
    {o1, o2} for the overloads in namespace std.
  • (21.2)
    {first + N, o1, o2} for the overloads in namespace ranges.
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Complexity: At most last - first applications of pred and proj.
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template<class ForwardIterator, class Predicate> constexpr ForwardIterator partition_point(ForwardIterator first, ForwardIterator last, Predicate pred); template<forward_iterator I, sentinel_for<I> S, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> constexpr I ranges::partition_point(I first, S last, Pred pred, Proj proj = {}); template<forward_range R, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> constexpr borrowed_iterator_t<R> ranges::partition_point(R&& r, Pred pred, Proj proj = {});
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Let proj be identity{} for the overloads with no parameter named proj and let E(x) be bool(invoke(​pred, invoke(proj, x))).
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Preconditions: The elements e of [first, last) are partitioned with respect to E(e).
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Returns: An iterator mid such that E(*i) is true for all iterators i in [first, mid), and false for all iterators i in [mid, last).
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Complexity: applications of pred and proj.